


This Will Be Your Downfall

by NidoranDuran



Category: Digimon - All Media Types
Genre: Anal Sex, F/M, Incest, Mutual Masturbation, Plot What Plot/Porn Without Plot, Public Sex, Sibling Incest, Vaginal Sex
Language: English
Status: Completed
Published: 2020-11-30
Updated: 2020-11-30
Packaged: 2021-03-10 05:40:01
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 5,365
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27799354
Author URL: https://archiveofourown.org/users/NidoranDuran/pseuds/NidoranDuran
Summary: Tai gave his sister a cute choker for her birthday, and Kari's decided they can use it as a signal for when it's 'safe' for them to have some fun. When Tai sees Kari wearing it in all manner of unsafe places, he realizes just what a monster he's created. Anonymous commission.
Relationships: Yagami Hikari | Kari Kamiya/Yagami Taichi | Tai Kamiya
Comments: 2
Kudos: 64





	This Will Be Your Downfall

"What if I wear this whenever it's safe for us to fuck?' Kari asked, clinging tightly to her brother's chest as she worked up and down his cock, fumbling against his lips. She wore nothing but the choker he'd given her, a birthday gift along with the joy of getting pounded raw by her hung big brother. Those were the only gifts she needed. It was a black leather band with a heart charm in the middle, a perfect and adorable accessory that she was happy to wear for him, and happy to wear plenty more. As she clung to him and rode his lap harder, though, she got ideas, and let those ideas push her further, inducing senseless expressions of raw joy inside of her.

"What are you thinking?" Tai asked, hands on her butt as he encouraged her along in riding him, smile widening. He liked the idea just fine, intrigued and curious as he held tightly to the possibilities, as he let her work harder along his shaft and seek out more of this pleasure and passion. He worked eagerly to thrust up into her from below, meeting the clumsy lips and shameless excitement that kept pushing him. Fucking his sister was the sort of wrongness Tai should have given more pause to, but he found himself incapable of controlling any of that, desperately pounding into her and fucking her with clear desperation.

"I love this choker. It's so nice. But what if I only wear it when it's clear for you fuck me? We don't need to say anything, don't need mom to catch on. You can just grab hold of me and pound me wherever you see me. It's okay." She was focused. Hungry. Desperation burned up inside of her as she did her part to lean into this, and there was absolutely no controlling herself in this mad descent downward. Faster she bounced atop her brother's dick, always in such a state of eager hunger. "I can't just yell across the room that I want my brother's dick, but if I put it on, it means I want it, and you can come stick it in me without asking."

Thrusting faster up from below, Tai nodded, tugging her deeper into the feverish kiss, lost to the pleasure and the excitement. He loved the idea, and he didn't know how to hold back the reckless joys he felt pushing his limits. He craved more of whatever he could get from this mess, careless and greedy in his steady march toward desperation and hunger. Tai needed more of whatever this insanity was, and he didn't care about holding back his thrusts as he let it all take him by storm. "I love that. It's so hot." He pulled her down on top of him, tugging her to lie on his lap while he pushed on faster and stranger, embracing these shameless pleasures and passions with hopeless fever.

It was supposed to be a cute birthday present for her to wear whenever she wanted to, but Tai couldn't argue with the idea of her turning his present for her into a present for him, a signal she wanted some big brother dick. They sealed their deal the only way the siblings had come to know how to: throwing their weight behind utter ecstasy, Tai came inside of his little sister, made her gasp and shriek in joy against him as she melted into the heat and the warmth of his affection, accepting the incestuous creampie and losing herself to her own reckless climax in turn.  
****************************  
"Is that the choker Tai got you?" Yuuko asked her daughter as she put breakfast down in front of both of her kids. She smiled as she looked at Kari wearing it at breakfast. "You must really like it. and Tai, good job at finding something that's just Kari's style." She was happy to see them getting along as she went off to get plate up her own breakfast last.

Tai's eyes swung around in surprise. It hadn't even been a day since Kari instituted the 'code'. Had she just fucking forgotten already? He stared at her in surprise, not sure how to respond to Kari, and he knew he couldn't well ask her if she was really signaling for him to fuck her in front of their mom. She couldn't have been, right?

"I love it, mom. Maybe you should get one too." Leaning back with a big smile, Kari drew Tai's eyes lower, down to where she had her shorts undone, a clear invitation for him to reach his hand in, as she in turn fumbled around for his own, his lack of pants making it easy to get in under the leg of his boxers and grasp his dick. "It's such a nice collar."

"What are you doing?" Tai whispered, leaning in real close as he tried to avoid detection from their mother. But even as he did so, her free hand reached for his and guided it between her legs.

"I'm using the choker for what it was made for."

"It's not safe," he groaned. But even s he did so, he slipped some fingers under her shorts and began to rub at her needy pussy, frustrated that he was so weak and so helpless against Kari's indulgences and her desires, but he couldn't help it. He couldn't believe he was doing this, but he took the risk she asked for from him, accepting a weird twist around into bizarre indulgence, into hungers he didn't know how to control, but each step of the way he was simply powerless against her.

The coy, innocent teasing made what she did all the more wicked. Kari was unabashed about her greedy lusts for brother dick, as she stroked him with careful motions, her own thighs gently tightening around his hand to urge him on. "See?" she whispered, smile brighter as she looked over to her mom. "What do you think mom? Do you want one, too? We can always ask Tai where he got his."

"I think it's a little bit too stylish for me," Yuuko insisted, brushing it off. But Kari wasn't looking to convince her stay at home mother to wear more chokers, and her response was still drawing attention to it, still making Tai squirm as she jerked him off.

Yuuko remained blissfully unaware that her children were jerking one another off under the table. All she focused on was eating dinner, the happy family breakfast a completely normal and not insane thing that absolutely was not going awry outside of view. She sat there, noting how close they were sitting, but simply happy that they were getting close, that they were spending so much time together and enjoying themselves so much. It was a joy to see them both get along like they did, to know they could be friends. It was so heartwarming to see. Not that they had ever been at odds with one another, but still; she wanted to see them do more to be siblings and get along with each other.

But under the table, the steady ministrations of Tai's fingers into Kari's slick pussy, paired with Kari's strokes along Tai's cock, had both of them struggling. The desire to let loose and melt under the warmth and satisfaction of giving completely in to the other's touch was a maddeningly enticing treat. Tai took it a bit harder than Kari did, owing to how completely unprepared he was to deal with any of this pressure, struggling now to focus on how many ways all these emotions tore through him at once. It was all too much to bear, and his nerves threatened to get the better of him as he squirmed in place, too embarrassed to think clearly, losing ground and not having a prayer of dealing with any of it.

"Tai, are you okay?" Yuuko asked, looking at her fidgety son and wondering if something was amiss. "You look flush. Are you feeling okay?"

"Yeah, I'm fine!" Tai said. A bit too fast. A bit too loud. "I just slept under a lot of blankets all night. Feel really hot. It's okay." But he was a squirmy mess only getting more fitful and concerned as his sister beat him off. He couldn't look his other in the eye, doubly so while his fingers probed deep into his sister's twat and gave up to the weirdness and the passion of this moment. He found himself aflame with way too much excitement to deal with, and he was powerless to stop it.

Kari's thighs spread out further, hips rolling as she brought some food to her mouth to hide the way she whispered, "Make me cream my shorts, big brother." She knew it would drive him mad. 'Big brother' took on entirely new meanings when they were fucking, and he couldn't contain himself. Tai had to cram some toast into his mouth to avoid groaning out too loudly as he nutted inside of his boxers, blowing his load into a fresh pair of underwear and ruining them for the rest of his day with a gooey, sticky load. His fingers fumbled and toyed around harder in Kari's hole, and she didn't need much longer either, giving in to the pleasure with such confident delight and a firmness that had her twisting underneath his touch. It felt too good for Kari to handle, and she wriggled about in raw, drunken ecstasy under his touch.

"Well, if you do feel bad, you should let me know, okay?" Yuuko frowned. "I worry about you kids. But I trust you to know how you feel."

"Thanks mom. It's fine, but thanks.," Tai tried not to pant too hard as he sat there confused and frustrated, burning up with way too many feelings to deal with. He looked over to Kari, whose big smile seemed so maddeningly smug that he wanted to fuck the look off of her face. But that was only giving her what she wanted, wasn't it?  
******************************  
TK was with his dad that week, which meant he and Matt were under the same roof, and when it came to Kari hanging out with him and Tai hanging out with Matt, the siblings had to take the train over at the same time. That was fine enough as they headed off together, but there was one pretty big problem in the way of it all. When Tai wasn't looking, Kari slapped her choker on, and once he was looking again, she did everything she could to nudge it, to draw attention to it as they stood on the train together and she not so subtly demanded some attention right then and there.

Tai couldn't believe his eyes. "Again?" he asked, startled and a bit weary. "Do you know what 'safe' means?" He couldn't believe this.

Kari said nothing, biting her lip and turning around a little bit, sticking her perky butt toward him as she held onto the bar for stability. She was playing at driving him mad, and there was nothing Tai could do about it.

Well, he could have done nothing. He knew that was definitely an option here, and yet not an option he took, as his hands grasped at her backside and began to grope her. For one, he couldn't really resist the opportunity. For another, maybe feeling her up was the way forward; if Tai actually called her bluff and felt her up on the train, Kari might get cold feet. Might shirk away from everything he was doing and finally pulled away, admitting this was going too far. That was the hope, at least.

It was a pretty faint fucking hope. Tai wasn't even sure it would work, and indeed, as his hands eagerly toyed with her ass, getting up her skirt and groping her in public, Kari got way too excited to help herself. She ended up rising to her toes, struggling to contain herself as the molten excitement filled her up, and as Tai kept groping her, she felt like she was just getting rewarded for her misbehavior. Nothing about getting groped like this was even kind of a punishment, and Kari only felt the sweet joy of being touched, being used, and she wanted even more of it, growing more demanding and desperate as she let this all take hold of her.

Finally, Kari could take no more. Her as shoved back hard against Tai's lap in a show of fitful need. She didn't try to hide her desires, the desperate lust ripping trough her as she felt the passion hit her like a truck. "Fuck my ass, big brother," she whined, rubbing up against his lap with her perky butt, needy and hopeless and completely incapable of dealing with how badly she craved this. It was a need beyond sense, her behind grinding away at him. She could feel his erection. He wasn't exactly soft in the face of this all, and Kari knew he wanted it too, whether he admitted it or not

Powerless against what ripped through him, Tai couldn't resist her whines any longer. He pulled his cock out, tugging her panties down and trying to shift about hastily, not wanting anyone to find him sticking his dick in any girl on the train. Even if they didn't know he was her brother, this was inappropriate, and he didn't want to be taken for one of those train perverts. He wasn't that at all. He was a perfectly normal, upstanding young man sinking his dick into his little sister's ass. Not a creep.

"Let's do this quickly, he groaned, trying his best to be done with this just as quickly as it had begun. That was easier said than done, given the weight of utter weirdness upon him now. Back and forth his hips worked, ready to seek out all the runaway emotions hitting him as he wound up for this. Steady strokes back and forth brought him a steady, tight desire to see this all through, to get Kari off and sate her weird desire to keep this all up. He didn't know why she was trying to take all these risks, but he didn't feel like he really had the strength and firmness to come down on her as much as he wanted to.

Instead, he found himself quite hopelessly stuck working to keep a groove and a peace that he failed miserably to attain. Kari worked back against him with erratic, eager motions that did very little to hide what she was doing. Perhaps in exchange for her overall silence, as all of these pleasures grew needier and messier out of control. Kari's ass craved her brother's dick, and she would not be quiet or calm about any of it, pushing back to meet his thrusts and pursuing all of the shameless heat and rising need pushing her closer to oblivion. Each push of her hips back to accept this treatment was a declaration of intent, and the idea that Tai was even control of this situation felt questionable.

At least she wasn't making noise. That wasn't much help, but it was also the biggest help, as he tried to avoid detection in the way he fucked her, lost in this clumsy heat and a fever that he didn't know how to deal with. Everything that Tai did to his sister's hole was another step deeper into utter confusion, and the compromising heat bubbling up through him as he fucked faster felt like a sharp lesson in how to land in mountains of shit if anything went wrong. At a second's sweep, anyone's head could have turned, anybody's attention could have undermined anything, and what could Tai had done about it? He was stuck here, struggling against the weight of utter confusion, and he didn't feel like anything was going to save him now from utter unraveling.

The snug, warm embrace of Kari's ass around his cock felt so good that Tai kept having to remind himself this was a dangerous place to be fucking. He wanted to melt into this ecstasy, struggling not to completely come undone as he leaned into all of this. It was a lot to deal with. Probably too much. The sharpest, strangest excesses of the moment left him with no clear idea what he was supposed to do about it, giving up harder to these feelings, struggling to control himself. Fucking Kari's ass just felt too good, and Tai was powerless against its allure, gripping her hip and tugging her back against him. he gave in to this all so readily, lost to the undermining fever of a certainty pushing him over the line. Tai wasn't strong enough. Wasn't steady enough. He was doomed to stumble through cycles of utter desperation again and again to no end, and all he could do was accept it.

Cumming inside was the only option, and Tai made sure that when he came, his hips pushed forward all the way, burying his cock balls deep into her so that not a single drop went anywhere but inside. It was one last hopeful push into the deep end, desperate to satisfy one final shred of reason and desperation. Kari couldn't deal with it, coming undone and struggling to contain herself as lost herself, and Tai knew it was a risky move, but he put his hand over her mouth to muffle the inevitable gasps of ecstasy. And they did follow, the rumble of noise and hot breath against his hand leaving Tai terrified as she let loose a bit too much spectacle.

"Do you want to get caught?" Tai hissed, slowly drawing his hand away as he pulled out of her, hastily tucking his cock away. Kari didn't straighten her panties out, though, and cum began to drip from her well fucked hole until he finally pulled them back in place, frustration rising even harder as he realized just how much she probably did.

Confirming his worst fears, Kari cooed, "Wouldn't that be hot?"

Before Tai could say or do anything, their stop came up, and rather than argue, Tai scrambled out of the train and ahead of Kari enough to not have to face the utter embarrassment of how deep he fell with each twist of her wicked aims against him.  
******************************  
"Yeah, I don't know why we got so much homework, either! I don't know how we're supposed to get that done. We have lives too, don't we?"

Kari was talking just a bit too loudly. Tai couldn't help but hear it all the way from his room. It was just the two of them home, and he figured she had just gotten way too noisy in her phone call. But as he slipped into the living room, ready to ask her to quiet down, he noticed her. Tiny shorts, tank top, lying on her stomach on the couch while she talked to her friend on the phone. But most vitally to all of this was that she wore the choker. It was plain as day around her neck, and Tai couldn't believe this. She looked at him, gave a wink, and signaled that she really was just talking loudly to fish him out of his bedroom.

Her ass rose up a little bit and wiggled toward him. Her shorts made her ass look ripe for the taking, barely coming down low enough to be considered decent to wear outside, but around the house, they were just perfect for relaxing and seducing horny older brothers. Tai was amazed, startled, and he almost fucking walked away, knowing that her obnoxious attempts at seduction were causing too much trouble.

But he was weak. More than weak, he felt like it was time he fuck a lesson into Kari. If shew wanted to cause problems and try to bait him into fucking her at inopportune times, he'd make sure she got too much of a good thing.

He strode over to the couch and tugged her shorts down, climbing up behind her and guiding her into a doggy style position for him. She gave him a bit of difficulty, but a firm slap across her ass made her respond, made her even yelp a bit in surprise. She tried to hide it by saying, "What did you just say? Really? No, that can't be true." She was going to cover for this as long as she could.

Lining up his shot, Tai rammed his cock up her ass, and where the other day on the train Tai had been pretty lax and slow about fucking her, so as not to draw too much attention, he was all out of fucking patience with her now. His hips slammed brutally forward, and he drew back just as hard, ready to pound her ass into hopeless submission and make his claim now over her.

The marked lack of sense or control in how he took her was everything Kari wanted, though. Her voice caught in her throat as she felt the brutality it her, the rush of senseless pleasure starting up through her body as Tai took to pounding his lesson into her. It was exactly what she needed, hitting the mark on the cravings that ripped through her veins as she welcomed him to take her by storm. Her conversation on the phone continued, and she was prepared to do everything she could to fight against her steepest temptations, prepared to keep tight and controlled, ready to make Tai work for the thrill of shutting her up.

Tai was ready to push as hard as he could for that very task. Wild slams forward tried to pound a lesson into his slutty sister, hands tightening on her hips as he worked for this. He didn't say anything, trying not to ruin the phone call as he let her dig her own grave with the conversation she kept trying to have. If she wasn't going to hang up, he wasn't going to make her. At least not by doing anything too obnoxious; he'd force her to hang up by pounding her senseless until she gave up fully to the chaos all of her own accord, a much better way to break her down and push her buttons. It seemed too good to be true, but he felt ready to keep up the pace, ready to break her down and teach Kari the harsh lesson she needed to learn, however hard she needed to learn it.

Having her brother's cock ravaging her ass like this was everything she wanted. Everything, all at once, pushing her buttons and her limits, sending her into a hazy crash too vocal and too ferocious to deal with. Kari couldn't believe how tightly she'd wound him up, feeling Tai work through all of his aggressions to a degree that had her barely able to handle it all. He was merciless, shameless, and she didn't have a prayer against him. "That's crazy. Did you say anything?" Kari was barely hanging onto the call, and everything she did say was simply a hopeful push to her friend to keep talking so that she didn't have to.

Even speaking up in that limited a capacity felt like a tall ask. It was too much, and every step of the way, Kari felt less capable, less in control of her voice. The struggle to stay tight and to avoid making too much noise took a toll on her, wearing her down harsher and steeper as she struggled more and more with each passing second. It was too much, and she was stuck here, struggling under the weight of this panic, a baffling mess of emotions all leaving her clueless and struggling, aching for sensations and releases that she didn't really know how to handle. It was too much, and all the while, the brutal slam of Tai's cock pounding her so deep brought her satisfactions she could barely keep sensible through. When she wasn't talking, she started burying her face into the couch cushion to try and silence herself and muffle the little noises squeaking out of her despite her best efforts.

Groping at her rear while he used her rougher and faster, all Tai wanted was to get his, to prove he was capable of teaching her a lesson and capable of making Kari bend for his intentions. He was strong, capable of doing everything he could do to make his sister bend to his will, and he didn't care about anything else on the path to it, desperate to find the satisfaction that eluded him, ready to ride her ass to the bitter end, and to take her down with him.

The struggles to keep quiet were rapidly approaching degrees she couldn't even begin to handle, struggling to not howl out in joy as he pushed her over the edge, and ultimately, Kari was powerless against it. She came undone, shrieking and gasping in messy ecstasy as she lost all sense, squeals of dizzy, hopeless joy ripping through her as she let herself go. She hid it in laughter, outrageously loud and hysterical laughter., "That's so funny!" she shouted with the same intonation she would have begged her brother to cum inside of her, and she all but was as she unraveled. Tai flooded her tight ass with his cum, and she couldn't even feign at keeping her head on straight a moment longer. She was simply a wreck. "I have to go."

Kari hung up. She realized too late that she didn't even say bye first, something she'd have to apologize for with some excuse when she got the chance. But for now, she looked over her shoulder, wondering what to say to Tai. "Big brother, did yo--"

Tai wasn't having any of that. He moved quickly, pulling out of Kari, turning her around ,and pinning her onto her back. He shoved his legs up so her knees were in her shoulders, folding her in half before he rammed his way right into her twat. "Don't try to play coy anymore," he snarled, and immediately took to fucking Kari as hard as he could. He didn't want to control himself, doing everything in his power to push her limits and break her down. After so long spent holding it all in, Kari was a hysterical wreck moaning, as an even rougher round started up. "Admit what you're doing."

"I'm getting my brains fucked out by my brother's huge cock!" she shrieked. It earned her a slap across the face. Kari couldn't believe it. Tai usually had to be coaxed into getting rough with her, and that level of roughness was a further expression of his needs still than anything she had felt before. And yet it was so unbearably hot that she could help but howl out in joy, pussy clenching down around his cock even tighter. "Slap me like that again!"

"I want you to admit what you're doing with the choker," he said, hammering faster into her. He didn't care about holding back now. He was too pent up and tense to even begin controlling himself.

"I'm just wearing it when I want you to fuck me," Kari whined, as if that was a perfectly innocent and normal thing to do. "I can't help if I'm a slut for my big brother's fat cock! I want it inside me all the time. If I could get away with it, I'd have you fuck me everywhere! And you can't pretend you don't like it. You came so much harder getting jerked off at the table than you ever do with my hand normally. And when you fucked me on the train, you filled my guts up so much that I had to keep hiding away in the bathroom to clean up. You love fucking your slutty sister in as many places as you can, don't lie. It feels good, doesn't it?" She was a fitful, tempestuous mess, noisily expressing the joys of what she was able to do and give in to here, and she knew she could get away with all of it.

The hardest part of wanting to be mad at Kari was that she was right. Tai was powerless against the reality of how sorely he craved more of this, hammering faster and rougher down into her, incapable of acting like he was strong enough to contain himself. With brutal, desperate speed, he fucked Kari, intent on proving a point, but that point felt further and further away as he came undone at the seams, doing everything he could to pound into her. "Fuck," he groaned. He didn't try to fight it. He didn't argue against her. He just fucked harder.

"I knew it! Big bro's addicted to fucking his little sister. I'm going to keep wearing this choker. You'll see me at your games with it. When you're out with friends, you'll see me walk by wearing it, and just have to drag me into an alley to fuck my throat. When we visit family, I'll slip it on, flutter my eyelashes at you, and you'll drag me into grandma's bathroom to rail me. You know you love this as much as I do, I'm just the one willing to admit it!" She was an inconsolable wreck, chaotic and feverish and aflame with so much desperate fire and passion that it felt almost too insane to be real. Tai couldn't handle any of this desire, but it didn't matter. He threw himself into the deep end, abandoned sense and restraint to give in completely, and he couldn't believe how good it felt to admit, even implicitly, how right she was.

The thrill of pinning Kari down to the couch and pumping her womb full of cum was everything to Kari. "My hole," he growled, as Kari squealed with joy for him to fill her up. He couldn't resist it. Couldn't argue against her allure. It was everything he craved all in one perfect, perky package. Kari was his perfect woman, and even if it was wrong to keep fucking her, he knew he was going to keep doing it, knew he was powerless against her.

Kari dizzily squealed and heaved, leaning tight against him and moaning softly, "My brother," as she tugged him down into a kiss and sought more of his affections. Yuuko wouldn't be home for a few hours. They had plenty of time to themselves.  
************************  
Tai was just showing off at this point. He'd run circles around the other guys, and now he was doing tricks with the ball, bouncing it between his heels and keeping it in the air, out of reach of the others as they tried to play the game, but he was flaunting his skills now, working up Davis in particular into a storm of frustration as he did what he could to avoid giving up the ball to him at all. When he decided he'd had enough, Tai jumped up, giving the ball a headbutt, and the surprise worked against the goalie, who had grown just as surprised by the antics, and was powerless to catch it as it sailed right by him.

Noise started up. Mostly led by Davis wondering if that was allowed, but it was just a pickup game at the park; there was no official rule book here, and Tai smirked as he looked around, about to speak up in his own defense when he saw, just past the fence around the soccer field, Kari standing there in a white sundress and, most fittingly, the black choker. She waved him toward the trees with a coy smile.

"Know what? I'll put myself in time-out, it's fine. Red card me, I'll be back for next game." Tai walked off, ignoring the calls of confusion from the others as he simply headed out of the soccer field to everybody's utter bafflement. It didn't matter; soccer was fine. But throatfucking his sister while she squatted down and fingered herself was even better.

**Author's Note:**

> If you enjoyed this depravity, why not follow me on twitter https://twitter.com/nidoran_duran and get updates on my new and upcoming stories?


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